One of the key components of any computer system is a place to store data. One common place for storing data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc. The magnetic transducer translates electrical signals into magnetic field signals that actually record the data “bits.”
The transducer is typically housed within a small ceramic block called a slider. The slider is passed over the rotating disc in close proximity to the disc. The transducer can be used to read information representing data from the disc or write information representing data to the disc. When the disc is operating, the disc is usually spinning at relatively high revolutions per minute (“RPM”). A current common rotational speed is 7200 RPM. Rotational speeds in high-performance disc drives are as high as 15,000 RPM. Higher rotational speeds are contemplated for the future.
The slider is usually aerodynamically designed so that it flies on the cushion of air that is dragged by the disc. The slider has an air-bearing surface (“ABS”) which includes rails and a cavity or depression between the rails. The air-bearing surface is that surface of the slider nearest the disc as the disc drive is operating. Air is dragged between the rails and the disc surface causing an increase in pressure which tends to force the head away from the disc. Simultaneously, air rushing past the cavity or depression in the air-bearing surface produces a lower than ambient pressure area within the cavity or depression. This sub-ambient pressure counteracts the pressure produced at the rails. The opposing forces equilibrate so the slider flies over the surface of the disc at a particular fly height. The fly height is the thickness of the air lubrication film or the distance between the disc surface and the transducing head. This film minimizes the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation.
Information representative of data is stored on the surface of the memory disc. Disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held accurately during a read or write operation using the servo information.
The best performance of the disc drive results when the slider is flown as closely to the surface of the disc as possible. In operation, the distance between the slider and the disc is very small; currently “fly” heights or head media spacing is about 0.5-1 micro inches. The constant demand for increasing hard drive recording density has resulted in a drastic decrease in head media spacing (HMS) over the years. Variation in the HMS of fly height due to altitude or manufacturing variation-induced fly loss, is now an increasing source of problems due to head/media intermittent contact, especially at sub half-micro inch fly height. Intermittent contact induces vibrations detrimental to the reading/writing quality at such low fly height. Intermittent contacts may also eventually result in a head crash and total loss of data, which, of course, is very undesirable.
Slider air bearings possess three degrees of freedom; namely vertical motion, pitch rotation and roll rotation. Associated with the three degrees of freedom are three applied forces, a pre-load force imposed by the gimbal, an air-bearing suction force, and an air-bearing lift force. Steady state fly altitude of the entire slider is achieved when these three forces balance each other. Previous studies have shown a strong relationship between suction force center position and altitude sensitivity. On the one hand, lower ambient pressure will generate both loss from lift force and suction force but by different amounts, thereby having the slider reaching equilibrium with the pre-load force at lower or higher overall fly height. On the other hand, the component that will dictate the actual PTFH (pole tip fly height) loss or gain, is rotation of the slider around the pivot point (Xcg) (See FIG. 5 which is a free body diagram of slider with forces). It is generally acknowledged that the closer the suction force center is towards the leading edge (Xn<Xcg, FIG. 1), the more pitch variation that occurs when the suction force is lost or varies. Simply put, the loss of suction rotates the slider counter clockwise in the pitch direction and makes the fly loss worse. On the other hand, rotating the slider clockwise and compensation of the global fly loss can be achieved with Xn>Xcg, even to a point where PTFH can increase with altitude.
What is needed is a slider air-bearing design for low altitude sensitivity. What is also needed is a design for controlling suction force center location. However, this has to be achieved without decreasing lift and suction magnitude, which could degrade other performance characteristics such as bearing stiffness and manufacturing sensitivity.